A Hybrid Numerical Wave Model for Extreme Wave Kinematics

Abstract

Numerical wave model that predicts realistic and correct wave kinematics such as wave elevation and particle velocity for the ocean waves become an essential part of the offshore platform design. A recent joint-industry effort, ‘Reproducible Offshore CFD JIP’, presented a systematic procedure to qualify the wave models and several wave models that satisfy the proposed qualification criteria. To name a few, Higher-Order Spectral Method (HOS, HOSM), HAWASSI, IGN, Reef3D::FNPF and TPNWT wave models have been verified for moderate to extreme sea states. They are all based on potential theory with an empirical wave-breaking model implemented. In this paper, the numerical methods of the existing wave models are compared to derive a new numerical wave model combining superior features of them. The new model uses pseudo-spectral method that is used in the HOS / HOSM and HAWASSI for the time evolution of the surface variables — surface elevation and free-surface velocity potential, but the variational method for the Laplace equation for fluid volume that is used in IGN and TPNWT. The new hybrid model shows efficiency and accuracy of the spectral method and the robustness of the variational method. The new numerical model is verified following the qualification criteria proposed in the ‘Reproducible Offshore CFD JIP’. The verification results of the new model show both robust convergence behavior and efficiency in practical numerical setup.